The selection process, which corresponds conceptually to the main organization of patterns, continues during the next 4—5 years and ends around early adolescence.
This lack of synchrony among cortical regions may also occur upon individual cortical neurons where different inputs may mature at different rates see Juraska, , on animal studies. After the cycle of synapse overproduction and selection has run its course, additional changes occur in the brain.
They appear to include both the modification of existing synapses and the addition of entirely new synapses to the brain. Research evidence described in the next section suggests that activity in the nervous system associated with learning experiences somehow causes nerve cells to create new synapses. Unlike the process of synapse overproduction and loss, synapse addition and modification are lifelong processes, driven by experience.
This process is probably not the only way that information is stored in the brain, but it is a very important way that provides insight into how people learn. Alterations in the brain that occur during learning seem to make the nerve cells more efficient or powerful. Animals raised in complex environments have a greater volume of capillaries per nerve cell—and therefore a greater supply of blood to the brain—than the caged animals, regardless of whether the caged animal lived alone or with companions Black et al.
Capillaries are the tiny blood vessels that supply oxygen and other nutrients to the brain. In this way experience increases the overall quality. Using astrocytes cells that support neuron functioning by providing nutrients and removing waste as the index, there are higher amounts of astrocyte per neuron in the complex-environment animals than in the caged groups.
Overall, these studies depict an orchestrated pattern of increased capacity in the brain that depends on experience. Other studies of animals show other changes in the brain through learning; see Box 5.
The weight and thickness of the cerebral cortex can be measurably altered in rats that are reared from weaning, or placed as adults, in a large cage enriched by the presence both of a changing set of objects for play and exploration and of other rats to induce play and exploration Rosenzweig and Bennett, These animals also perform better on a variety of problem-solving tasks than rats reared in standard laboratory cages.
Interestingly, both the interactive presence of a social group and direct physical contact with the environment are important factors: animals placed in the enriched environment alone showed relatively little benefit; neither did animals placed in small cages within the larger environment Ferchmin et al. Thus, the gross structure of the cerebral cortex was altered both by exposure to opportunities for learning and by learning in a social context.
Are the changes in the brain due to actual learning or to variations in aggregate levels of neural activity? Animals in a complex environment not only learn from experiences, but they also run, play, and exercise, which activates the brain. The question is whether activation alone can produce brain changes without the subjects actually learning anything, just as activation of muscles by exercise can cause them to grow.
To answer this question, a group of animals that learned challenging motor skills but had relatively little brain activity was compared with groups that had high levels of brain activity but did relatively little learning Black et al.
There were four groups in all. What happened to the volume of blood vessels and number of synapses per neuron in the rats? Both the mandatory exercisers and the voluntary exercisers showed higher densities of blood vessels than either the cage potato rats or the acrobats, who learned skills that did not involve significant.
How do rats learn? The objects are changed and rearranged each day, and during the changing time, the animals are put in yet another environment with another set of objects.
These two settings can help determine how experience affects the development of the normal brain and normal cognitive structures, and one can also see what happens when animals are deprived of critical experiences. After living in the complex or impoverished environments for a period from weaning to rat adolescence, the two groups of animals were subjected to a learning experience. The rats that had grown up in the complex environment made fewer errors at the outset than the other rats; they also learned more quickly not to make any errors at all.
In this sense, they were smarter than their more deprived counterparts. And with positive rewards, they performed better on complex tasks than the animals raised in individual cages. It is clear that when animals learn, they add new connections to the wiring of their brains—a phenomenon not limited to early development see, e. But when the number of synapses per nerve cell was measured, the acrobats were the standout group.
Learning adds synapses; exercise does not. Thus, different kinds of experience condition the brain in different ways. Synapse formation and blood vessel formation vascularization are two important forms of brain adaptation, but they are driven by different physiological mechanisms and by different behavioral events.
Learning specific tasks brings about localized changes in the areas of the brain appropriate to the task. For example, when young adult animals were. When they learned the maze with one eye blocked with an opaque contact lens, only the brain regions connected to the open eye were altered Chang and Greenough, When they learned a set of complex motor skills, structural changes occurred in the motor region of the cerebral cortex and in the cerebellum, a hindbrain structure that coordinates motor activity Black et al.
These changes in brain structure underlie changes in the functional organization of the brain. That is, learning imposes new patterns of organization on the brain, and this phenomenon has been confirmed by electro-physiological recordings of the activity of nerve cells Beaulieu and Cynader, Studies of brain development provide a model of the learning process at a cellular level: the changes first observed in rats have also proved to be true in mice, cats, monkeys, and birds, and they almost certainly occur in humans.
Clearly, the brain can store information, but what kinds of information? The neuroscientist does not address these questions. Answering them is the job of cognitive scientists, education researchers, and others who study the effects of experiences on human behavior and human potential. Several examples illustrate how instruction in specific kinds of information can influence natural development processes. This section discusses a case involving language development.
Brain development is often timed to take advantage of particular experiences, such that information from the environment helps to organize the brain. The development of language in humans is an example of a natural process that is guided by a timetable with certain limiting conditions. A phoneme is defined as the smallest meaningful unit of speech sound.
Very young children discriminate many more phonemic boundaries than adults, but they lose their discriminatory powers when certain boundaries are not supported by experience with spoken language Kuhl, Native Japa-. It is not known whether synapse overproduction and elimination underlies this process, but it certainly seems plausible. The process of synapse elimination occurs relatively slowly in the cerebral cortical regions that are involved in aspects of language and other higher cognitive functions Huttenlocher and Dabholkar, Different brain systems appear to develop according to different time frames, driven in part by experience and in part by intrinsic forces.
But, as noted above, learning continues to affect the structure of the brain long after synapse overproduction and loss are completed. There may be other changes in the brain involved in the encoding of learning, but most scientists agree that synapse addition and modification are the ones that are most certain.
Detailed knowledge of the brain processes that underlie language has emerged in recent years. For example, there appear to be separate brain areas that specialize in subtasks such as hearing words spoken language of others , seeing words reading , speaking words speech , and generating words thinking with language.
Whether these patterns of brain organization for oral, written, and listening skills require separate exercises to promote the component skills of language and literacy remains to be determined. Download this page as a PDF. Top photo: Scientist Andy Shih is working on new types of imaging that might someday be sharp enough to detect the tiny clogs in blood vessels called microinfarcts. Read more about it.
What does experimenting with other animals tell us about people? Find out in our new Brain Basics article. Get the basics. Here are the basics. How do moods differ from emotions? Can you alter your mood safely? Not only is exercise good for your muscles and bones, but it is also an important part of keeping your brain healthy. A fact sheet for students grades Sign up for monthly email updates on neuroscience discoveries, Cerebrum magazine, and upcoming events.
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